Closure systems for packaging, e.g., food packaging, may be categorized into three general categories: (i) cohesives, (ii) pressure sensitive adhesive based closures, and (iii) mechanical closures. A cohesive is a class of material that has no tack or adhesion except to itself an example of a cohesive system is illustrated in U.S. Pat. No. 6,076,969. These materials are often used to attach and form secure closures in food packaging such as, for example, in candy bars. These closures are essentially “one use” closure systems that are not suitable for repeatedly opening and closing the package.
Many packages are provided with a closure system to allow for repeated opening and resealing of the package to protect the contents inside the package. Pressure sensitive adhesive-based closures and mechanical closures may be employed for such applications. Pressure sensitive adhesive systems have been provided as detackified adhesives where the intrinsic properties of the adhesive are manipulated to reduce the tack and peel adhesion (see, e.g., U.S. Pat. No. 5,346,766). For example, the modulus of the adhesive may be adjusted to reduce the initial tack and peel adhesion. In these types of adhesives, adhesion builds over time as the adhesive flows and recovers its intrinsic properties.
Pressure sensitive based closures are based on simple PSA tapes attached to one of the side package adhering to the substrate on the other side. In some of those cases, an adhesive is modified with an additive such as a cluster of particles, powders or talc on the surface to alter the initial tack and peel properties of the adhesive. There are cases of PSA systems wherein the surface is modified with glass particles such as in U.S. Pat. No. 5,141,790. Although such tapes or laminates are not used in food closure and packaging applications, in these systems, pressure is used to press in on the additive, e.g., the glass particles, to embed them into the adhesive bulk and the adhesion builds rapidly. A number of patents such as U.S. Pat. Nos. 4,376,151, 4,556,595, 3,331,279, and 3,314,838 all fall within this category to limit the initial adhesion and then activate the adhesion to a substrate by pressing down with pressure. These kinds of PSA laminates are used for industrial graphics applications such as the decoration of sides of trucks, etc. where the slidability of these large graphics on substrates is needed. A number of other patents, such as U.S. Pat. Nos. 6,541,098 and 5,871,607, deal with modification of the surface of a highly conformable film or substrate with a topology of upraised non-tacky regions and valleys with adhesive. These structures provide the non-tacky feel to the finger as it slides along the upraised non-tacky regions. On applying pressure, the finger then contacts the adhesives in the valleys building adhesion. These have been used for applications such as Glad Press n Seal.
In the afore mentioned adhesives, the adhesives are applied to one surface of the package and are suitable for adhering to another surface of the package that is free of any adhesive.
Mechanical systems include such items as Velcro, “zipper” systems, hook and loop, slider systems, “mushroom” type closures, and various male/female closure systems, etc., and are commonly used on packages to allow for opening and resealing or closing the package. Examples of such systems are illustrated in U.S. Pat. No. 7,857,515 (hook and loop), U.S. Pat. No. 7,736,058 (mushroom type), U.S. Pat. Nos. 7,316,052, 7,340,807, and U.S. Patent Publication No. 2011/0171430 (male/female closure systems). Such systems require careful alignment of the components to close the package correctly. Additionally, such systems are three-dimensional in character and add to the surface profile of the package. Mechanical systems are also typically expensive and difficult to manufacture and apply for certain types of packages.